Lipogenic processes are adaptive and vary with the level of dietary fat and/or carbohydrate. Fatty acid synthesis and associated enzymes in rat liver are also very dependent on type of dietary energy. Polyunsaturated fats are more effective inhibitors of lipogenic parameters in rats but such as effect in chicks remains unclear. In conflict with in vivo studies lipogenesis in isolated cells reportedly is most inhibited by saturated fatty acids. Because hepatocytes can be readily isolated from rats and chicks, they provide useful models for characterizing and correlating in vivo an in vitro effects of specific fatty acids on lipogenic rates. The objective is to resolve the conflicts between intact animals and isolated cells regarding fatty acid regulation of lipogenesis. The influence of dietary fat (particularly polyunsaturated) on kinetic behavior of key glycolytic and lipogenic enzymes will be quantitatively compared to the rate of decrease in fatty acid synthesis in vivo during the attainment of a new steady-state induced by diet change. Furthermore, the concentration of specific long chain fatty acids esterified to CoA and the level of key metabolite effectors in total liver tissue will be correlated to the rate of fatty acid synthesis. In vivo hepatic metabolism will be supported by metabolite concentrations and intracellular distribution (e.g. citrate) measurements in rat and chick hepatocytes exposed to exogenous fatty acids. The activity of citrate transport will be studied in mitochondria isolated from animals and cells eating or exposed to fatty acids differing in degree of unsaturation. Finally, the differential effects of type of dietary fat on rad adipose tissue lipogenesis will be examined. The mechanism by which dietary polyunsaturated fats regulate lipid metabolism will contribute to developing useful dietary management of hypertriglyceridemia and reveal common points of regulation which may be of more universal application.